The sensitivity of radiation-detecting semiconductor components can be improved by focusing the radiation to be detected in the light-sensitive zones. E.g., U.S. Pat. No. 6,221,687 and U.S. Pat. No. 6,362,498 disclose image sensors which contain integrated arrays of microlenses which serve to focus the received radiation on a photodiode. In the image sensors disclosed in those documents, color filters are employed to achieve sensitivity to particular wavelengths or colors. A similar component is disclosed in US 2002/0197763 A1.
Other embodiments of color-sensitive radiation-detecting semiconductor components are disclosed in U.S. Pat. No. 5,965,875 and US 2003/0038296 A1. In these components, the semiconductor bodies contain a plurality of radiation-sensitive p-n transitions which are disposed mutually vertically. The color sensitivity results from the fact that short-wave photons are preferentially absorbed in the upper zones of the semiconductor body, due to stronger absorption in the semiconductor, and photons with longer wavelength are preferentially absorbed in the deeper lying zones of the semiconductor body.
In the above-described radiation-detecting components, the focusing of the radiation is accomplished with refractive optical elements, which elements are substantially larger than the wavelength of the radiation.
For focusing and/or deflection of light, diffractive elements are known which are based on the principle of diffraction and which have structures of the order of magnitude of the light wavelength(s). An example of such a diffractive focusing element is a zone plate. Zone plates are used in particular in the area of technology of x-ray radiation, for focusing of radiation, where the use of lenses is impracticable because of the small differences in the index of refraction between different materials, and because of the high absorption. An example of such a use is an x-ray microscope disclosed in DE 364257 A1 [sic].
Zone plates are comprised of structures of concentric rings, with the widths of the rings decreasing with progression in the inward direction. In dimensioning of such zone plates, a distinction must be made between utilization of diffraction in the near-field region (Fresnel diffraction) and utilization of diffraction in the far-field region (Fraunhofer diffraction).
The engineering design and dimensioning of Fresnel zone plates is known from, e.g., Hecht, E., 1989, “Optik” (in English, “Optics”), published by Addison-Wesley. Further, a distinction is made between amplitude zone plates and phase zone plates. In amplitude zone plates the radiation of each second Fresnel zone is shielded by an absorbent material, whereas in a phase zone plate a path difference (difference in the path of the radiation) is produced between two neighboring zones in that the materials of the zones differ in index of refraction and/or thickness. With both types of zone plates, beneficial (“constructive”) interference occurs at the focal loci, the positions of which loci depend on the wavelength of the incident radiation.